Binarize an image

Question

I am sorry for image sizes.

Now these two cropped images I have in a dataset. I am going to feed these images into a machine learning algorithm. Before doing that, I want to extract binarized digits and feed the binary images into algorithm, instead of feeding directly. Can you please elaborate how can I achieve this kind of clean binarization ?

I found otsu and other thresholding methods but they were unable to give clear digits in image.

Answer 1

I had some success, though I don't know how it will fare with the rest of your images, using a 2-colour quantisation, conversion to greyscale and normalisation.

I just did it at the command line with ImageMagick, as follows:

convert input.png +dither -colors 3 -colors 2 -colorspace gray -normalize -scale 250x result.png

So, it loads an image and disables dithering, so that the subsequent quantisation only results in 2 actual colours rather than dithered mixtures. I then quantise down to 3 colours - still in RGB colourspace - and then further down to 2 colours. Then, I convert those 2 colours to greyscale and normalise them so the darker one becomes black and the lighter one becomes white.